The aluminum die casting industry spends an enormous amount of money each year replacing dies due to premature failure. Premature die failures are a result of erosive wear, corrosion/oxidation, soldering, and thermal fatigue. The die casting industry could recognize significant savings by reducing the number of premature die failures, and thereby replacement costs, while reducing downtime and environmental waste. It has been estimated that die life may be increased by as much as 3 to 100 times depending on the process cycle and aluminum alloy used.
Several coating companies provide wear resistant coatings for specific parts of a die casting machine such as core pins. Other coating solutions have been described in the literature although not all have found commercial acceptance. For example, in U.S. Pat. No. 6,333,103, the Japanese group Ishii et al. describe the use of an alpha-alumina system for use in coating tools, dies and metal melt-contacting members. U.S. Pat. No. 5,972,495 to the same Japanese group teach the use of alpha-alumina as a good coating for increasing wear resistance for cutting tools. U.S. Pat. Nos. 5,702,808; 5,766,782 and 5,851,687 to Ljungberg teach the use of a CVD alpha-alumina as a wear resistant coating for use in chip forming machining. U.S. Pat. No. 5,705,263 to Leander et al. discloses the use of a CVD alumina coated cemented carbide body to improve wear resistance of cutting tool inserts. U.S. Pat. No. 5,137,774 to Ruppi describes the use of a multi-purpose alumina system as a hard wear-resistant coating for milling and cutting both cast irons and steels. This coating incorporates the combined properties of kappa-alumina and alpha-alumina in the coating. U.S. Pat. No. 5,071,696 to Chatfield et al. discloses the use of CVD alumina in contact with TiC for increasing wear resistance in cutting inserts. U.S. Pat. No. 3,977,061 to the Swedish group Lindstrom et al. discloses the use of ceramic oxides to increase wear and toughness in sintered hard metal bodies (cutting inserts). U.S. Pat. No. 3,837,896 to the same Swedish group discloses using metallic carbides or metallic nitrides as a coating to improve wear resistance.
Despite these proposed means of strengthening die casting coatings, there is still a need for die casting equipment coatings having improved microstructure of the alumina to form a coating that displays good non-wettability with aluminum coupled with oxidation and wear resistance.